In recent years, increase in integration degree, higher information density, and higher image definition have been desired more and more in fields of optics and electronics. Therefore, a material used in these fields is strongly required to have a finer structure on its surface. Namely, forming a fine pattern structure (hereinafter referred to as fine patterning) has been strongly required. Additionally, in a field of research for a regenerative medicine, a film having a fine structure on its surface is effectively used as a scaffold for cell culture.
Various methods for the fine pattering have been put to practical use. For example, there are a deposition method using a mask, an optical lithography adopting photochemical reaction and polymerization reaction, a laser ablation technique, and the like. Additionally, according to Japanese Patent Laid-Open Publication No. 2006-070254, as the fine patterning, there is disclosed a method for forming a porous film having a plurality of pores from a solution.
The method for forming a porous film disclosed in Japanese Patent Laid-Open Publication No. 2006-070254 is briefly described hereinbelow. At first, a polymer solution containing a hydrophobic solvent and a polymer is applied to a support such that a coating film is formed on the support. The polymer solution is hereinafter referred to as solution. Next, wet gas is blown to an exposed surface of the coating film. The wet gas has temperature, dew point, condensation point of solvent vapor, and the like which are adjusted to be within a predetermined range. Water vapor is condensed from ambient air on the exposed surface to generate water drops. The water drops on the exposed surface are grown up. Note that, the water drops generated on the exposed surface enter an inside of the coating film while keeping its size or growing. At the end, dry gas is blown to the coating film to evaporate the solvent and the water drops from the coating film. In accordance with the evaporation of the water drops from the coating film, pores are made by the water drops as a template for the porous material on the coating film. Thus, the porous film having a plurality of pores can be formed from the solution.
The merit of the fine pattern structure obtained by the method disclosed in Japanese Patent Laid-Open Publication No. 2006-070254 lies in that it is possible to control the speed for cell culture more easily at lower cost by adjusting a pore diameter and a pitch of the pores in comparison with the fine pattern structure obtained by other kinds of fine patterning. If the fine pattern structure having the merit described above is disposed on a surface of a stent that is inserted into a blood vessel after a narrowed portion or an obstructed portion of the blood vessel is made open, it is possible to prevent restenosis of the blood vessel. Further, the fine pattern structure may be applied to not only the stent but also other medical devices to be disposed inside the human body, so as to achieve the advantageous effect as described above.
However, a surface of the stent or other medical devices such as catheter is generally not flat but curved. The fine patterning disclosed in Japanese Patent Laid-Open Publication No. 2006-070254 is limited to the fine patterning on a surface of a material in a sheet form. Therefore, the fine patterning disclosed in Japanese Patent Laid-Open Publication No. 2006-070254 is not suitable for a curved surface including the surface of the stent or other medical devices such as catheter.